package org.rency.common.utils.security;

import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.Signature;
import java.security.interfaces.DSAPrivateKey;
import java.security.interfaces.DSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

/**
 * DSA-Digital Signature Algorithm 是Schnorr和ElGamal签名算法的变种，被美国NIST作为DSS(DigitalSignature Standard)。简单的说，这是一种更高级的验证方式，用作数字签名。不单单只有公钥、私钥，还有数字签名。私钥加密生成数字签名，公钥验证数据及签名。如果数据和签名不匹配则认为验证失败！数字签名的作用就是校验数据在传输过程中不被修改
 * @author rencaiyu
 *
 */
public class DSAUtils {

	public static final String ALGORITHM = "DSA";  
	  
    /** 
     * 默认密钥字节数 
     *  
     * <pre> 
     * DSA  
     * Default Keysize 1024   
     * Keysize must be a multiple of 64, ranging from 512 to 1024 (inclusive). 
     * </pre> 
     */  
    private static final int KEY_SIZE = 1024;  
  
    /** 
     * 默认种子 
     */  
    private static final String DEFAULT_SEED = "0f22507a10bbddd07d8a3082122966e3";  
  
    private static final String PUBLIC_KEY = "DSAPublicKey";  
    private static final String PRIVATE_KEY = "DSAPrivateKey";  
  
    /** 
     * 用私钥对信息生成数字签名 
     * @param data 加密数据 
     * @param privateKey 私钥 
     * @return 
     * @throws Exception 
     */  
    public static String sign(byte[] data, String privateKey) throws Exception {  
        // 解密由base64编码的私钥  
        byte[] keyBytes = Base64Utils.decoder(privateKey).getBytes();  
        // 构造PKCS8EncodedKeySpec对象  
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);  
        // KEY_ALGORITHM 指定的加密算法  
        KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);  
        // 取私钥匙对象  
        PrivateKey priKey = keyFactory.generatePrivate(pkcs8KeySpec);  
        // 用私钥对信息生成数字签名  
        Signature signature = Signature.getInstance(keyFactory.getAlgorithm());  
        signature.initSign(priKey);  
        signature.update(data);  
        return Base64Utils.encoder(signature.sign());  
    }  
  
    /** 
     * 校验数字签名 
     * @param data 加密数据 
     * @param publicKey 公钥 
     * @param sign 数字签名 
     * @return 校验成功返回true 失败返回false 
     * @throws Exception 
     */  
    public static boolean verifySign(byte[] data, String publicKey, String sign) throws Exception {  
        // 解密由base64编码的公钥  
        byte[] keyBytes = Base64Utils.decoder(publicKey).getBytes();  
        // 构造X509EncodedKeySpec对象  
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);  
        // ALGORITHM 指定的加密算法  
        KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);  
        // 取公钥匙对象  
        PublicKey pubKey = keyFactory.generatePublic(keySpec);  
        Signature signature = Signature.getInstance(keyFactory.getAlgorithm());  
        signature.initVerify(pubKey);  
        signature.update(data);  
        // 验证签名是否正常  
        return signature.verify(Base64Utils.decoder(sign).getBytes());  
    }  
  
    /** 
     * 生成密钥 
     * @param seed 种子 
     * @return 密钥对象 
     * @throws Exception 
     */  
    public static Map<String, Object> initKey(String seed) throws Exception {  
        KeyPairGenerator keygen = KeyPairGenerator.getInstance(ALGORITHM);  
        // 初始化随机产生器  
        SecureRandom secureRandom = new SecureRandom();  
        secureRandom.setSeed(seed.getBytes());  
        keygen.initialize(KEY_SIZE, secureRandom);  
        KeyPair keys = keygen.genKeyPair();  
        DSAPublicKey publicKey = (DSAPublicKey) keys.getPublic();  
        DSAPrivateKey privateKey = (DSAPrivateKey) keys.getPrivate();  
        Map<String, Object> map = new HashMap<String, Object>(2);  
        map.put(PUBLIC_KEY, publicKey);  
        map.put(PRIVATE_KEY, privateKey);  
        return map;  
    }  
  
    /** 
     * 默认生成密钥 
     * @return 密钥对象 
     * @throws Exception 
     */  
    public static Map<String, Object> initKey() throws Exception {  
        return initKey(DEFAULT_SEED);  
    }  
  
    /** 
     * 取得私钥 
     * @param keyMap 
     * @return 
     * @throws Exception 
     */  
    public static String getPrivateKey(Map<String, Object> keyMap) throws Exception {
        Key key = (Key) keyMap.get(PRIVATE_KEY);  
        return Base64Utils.encoder(key.getEncoded());  
    }  
  
    /** 
     * 取得公钥 
     * @param keyMap 
     * @return 
     * @throws Exception 
     */  
    public static String getPublicKey(Map<String, Object> keyMap) throws Exception {  
        Key key = (Key) keyMap.get(PUBLIC_KEY);  
        return Base64Utils.encoder(key.getEncoded());  
    }
    
    public static void main(String[] args) throws Exception {
    	String inputStr = "abc";  
        byte[] data = inputStr.getBytes();  
  
        // 构建密钥  
        Map<String, Object> keyMap = initKey();  
  
        // 获得密钥  
        String publicKey = getPublicKey(keyMap);  
        String privateKey = getPrivateKey(keyMap);  
  
        System.out.println("公钥:\r" + publicKey);  
        System.out.println("私钥:\r" + privateKey);  
  
        // 产生签名  
        String sign = sign(data, privateKey);  
        System.out.println("签名:\r" + sign);  
  
        // 验证签名  
        boolean status = verifySign(data, publicKey, sign);  
        System.out.println("状态:\r" + status);  
	}
	
}